Methods and Apparatus for Supporting Inter-Frequency Measurements

ABSTRACT

A radio network node receives an indication from the user equipment that the user equipment is going to perform an inter-frequency measurement for positioning, which inter-frequency measurement requires measurement gaps. The radio network node may determine a measurement gap pattern for performing the inter-frequency measurement and may signal, to the user equipment, information to initiate use of the determined measurement gap pattern in the user equipment. Alternatively the user equipment configures the measurement gap pattern itself based on a set of pre-defined rules.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/471,073, which was filed on Mar. 28, 2017, which applicationis a continuation of U.S. patent application Ser. No. 15/173,882, whichwas filed on Jun. 6, 2016 and issued as U.S. Pat. No. 9,635,637 on Apr.25, 2017, which application is a continuation of U.S. patent applicationSer. No. 14/591,146, which was filed on Jan. 7, 2015 and issued as U.S.Pat. No. 9,414,349 on Aug. 9, 2016, which application is a continuationof U.S. patent application Ser. No. 13/697,252, which was filed on Nov.9, 2012 and issued as U.S. Pat. No. 8,965,414 on Feb. 24, 2015, which isa national stage application of PCT/SE2011/050519, filed Apr. 28, 2011,and claims benefit of U.S. Provisional Application 61/333,007, filed May10, 2010, the disclosures of each of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

This invention relates in general to inter-frequency measurements inwireless communication networks and in particular to the signalingsupport for such measurements in wireless network architectures thatutilize signal measurements from multiple cells for e.g. positioning,location, and location-based services.

BACKGROUND

The Universal Mobile Telecommunication System (UMTS) is one of the thirdgeneration mobile communication technologies designed to succeed GSM.3GPP Long Term Evolution (LTE) is a project within the 3^(rd) GenerationPartnership Project (3GPP) to improve the UMTS standard to cope withfuture requirements in terms of improved services such as higher datarates, improved efficiency, and lowered costs. The Universal TerrestrialRadio Access Network (UTRAN) is the radio access network of a UMTS andEvolved UTRAN (E-UTRAN) is the radio access network of an LTE system. Inan E-UTRAN, a wireless device such as a user equipment (UE) 150 a iswirelessly connected to a radio base station (RBS) 110 a commonlyreferred to as an evolved NodeB (eNodeB), as illustrated in FIG. 1 a.Each eNodeB 110 a, 110 b serves one or more areas each referred to ascells 120 a, 120 b, and are connected to the core network. In LTE, theeNodeBs 110 a, 110 b are connected to a Mobility Management Entity (MME)(not shown) in the core network. A positioning server 140, also called alocation server, in the control plane architecture in FIG. 1a isconnected to the MME. The positioning server 140 is a physical orlogical entity that manages positioning for a so called target device,i.e. a wireless device that is being positioned. The positioning serveris in the control plane architecture also referred to as an EvolvedServing Mobile Location Center (E-SMLC). As illustrated in FIG. 1a , theE-SMLC 140 may be a separate network node, but it may also be afunctionality integrated in some other network node. In a user planearchitecture, the positioning is a part of a Secure User Plane Location(SUPL) Location Platform (SLP). The positioning server may be connectedto radio network nodes via logical links while using one or morephysical connections via other network nodes e.g., the MME. A NetworkManagement (NM) or Operations and Maintenance (O&M) node 141 may beprovided to perform different network management operations andactivities in the network.

The possibility of identifying user geographical location in a networkhas enabled a large variety of commercial and non-commercial services,e.g., navigation assistance, social networking, location-awareadvertising, emergency calls, etc. Different services may have differentpositioning accuracy requirements imposed by an application. Inaddition, some regulatory requirements on the positioning accuracy forbasic emergency services exist in some countries, e.g., FCC E911 in theU.S.

Three key network elements in an LTE positioning architecture are aLocation Services (LCS) Client, an LCS target and an LCS Server. The LCSServer is a physical or logical entity managing positioning for a LCStarget device by collecting measurements and other location information,assisting the terminal in measurements when necessary, and estimatingthe LCS target location. The LCS Client is a software and/or hardwareentity that interacts with the LCS Server for the purpose of obtaininglocation information for one or more LCS targets, i.e. the entitiesbeing positioned. The LCS Clients may reside in the LCS targetsthemselves. An LCS Client sends a request to the LCS Server to obtainlocation information, and the LCS Server processes and serves thereceived requests and sends the positioning result and optionally avelocity estimate to the LCS Client. A positioning request can beoriginated from a terminal or the network.

Two positioning protocols operating via the radio network exist in LTE,LTE Positioning Protocol (LPP) and LPP Annex (LPPa). The LPP is apoint-to-point protocol between a LCS Server and a LCS target device,used in order to position the target device. LPP can be used both in theuser and control plane, and multiple LPP procedures are allowed inseries and/or in parallel thereby reducing latency. In the controlplane, LPP uses RRC protocol as a transport.

LPPa is a protocol between eNodeB and LCS Server specified mainly forcontrol-plane positioning procedures, although it still can assistuser-plane positioning by querying eNodeBs for information and eNodeBmeasurements. Secure User Plane (SUPL) protocol is used as a transportfor LPP in the user plane. LPP has also a possibility to convey LPPextension messages inside LPP messages, e.g., currently Open MobileAlliance (OMA) LPP extensions (LPPe) are being specified to allow, e.g.,for operator- or manufacturer-specific assistance data or assistancedata that cannot be provided with LPP or to support other positionreporting formats or new positioning methods. LPPe may also be embeddedinto messages of other positioning protocol, which is not necessarilyLPP.

A high-level architecture, as it is currently standardized in LTE, isillustrated in FIG. 2, where the LCS target is a terminal 200, and theLCS Server is an E-SMLC 201 or an SLP 202. In the figure, the controlplane positioning protocols with E-SMLC as the terminating point areshown by arrows 203, 204 and 205, and the user plane positioningprotocol is shown by arrows 206 and 207. The SLP 202 may comprise twocomponents, SUPL Positioning Centre (SPC) and SUPL Location Centre(SLC), which may also reside in different nodes. In an exampleimplementation, the SPC has a proprietary interface with the E-SMLC 201,and an LIp interface with SLC, and the SLC part of SLP communicates witha PDN-Gateway (P-GW) (not shown) and an external LCS Client 208.

Additional positioning architecture elements may also be deployed tofurther enhance performance of specific positioning methods. Forexample, deploying radio beacons is a cost-efficient solution which maysignificantly improve positioning performance indoors and also outdoorsby allowing more accurate positioning, for example, with proximitylocation techniques.

UE positioning is a process of determining UE coordinates in space. Oncethe coordinates are available, they may be mapped to a certain place orlocation. The mapping function and delivery of the location informationon request are parts of a location service which is required for basicemergency services. Services that further exploit a location knowledgeor that are based on the location knowledge to offer customers someadded value are referred to as location-aware and location-basedservices. The possibility of identifying a wireless device'sgeographical location in the network has enabled a large variety ofcommercial and non-commercial services, e.g., navigation assistance,social networking, location-aware advertising, and emergency calls.Different services may have different positioning accuracy requirementsimposed by an application. Furthermore, requirements on the positioningaccuracy for basic emergency services defined by regulatory bodies existin some countries. An example of such a regulatory body is the FederalCommunications Commission regulating the area of telecommunications inthe United States.

In many environments, a wireless device position can be accuratelyestimated by using positioning methods based on Global PositioningSystem (GPS). Nowadays, networks also often have a possibility to assistwireless devices in order to improve the device receiver sensitivity andGPS start-up performance, as for example in an Assisted-GPS (A-GPS)positioning method. GPS or A-GPS receivers, however, may not necessarilybe available in all wireless devices. Furthermore, GPS is known to oftenfail in indoor environments and urban canyons. A complementaryterrestrial positioning method, called Observed Time Difference ofArrival (OTDOA), has therefore been standardized by 3GPP. In addition toOTDOA, the LTE standard also specifies methods, procedures, andsignaling support for Enhanced Cell ID (E-CID) and Assisted-GlobalNavigation Satellite System (A-GNSS) positioning. In future, Uplink TimeDifference of Arrival (UTDOA) may also be standardized for LTE.

OTDOA Positioning

Wth OTDOA, a wireless device such as a UE measures the timingdifferences for downlink reference signals received from multipledistinct locations. For each measured neighbor cell, the UE measuresReference Signal Time Difference (RSTD) which is the relative timingdifference between a neighbor cell and the reference cell. Asillustrated in FIG. 3, the UE position estimate is then found as theintersection 430 of hyperbolas 440 corresponding to the measured RSTDs.At least three measurements from geographically dispersed RBSs 410 a-cwith a good geometry are needed to solve for two coordinates of the UE.In order to find the position, precise knowledge of transmitterlocations and transmit timing offsets is needed. Position calculationsmay be conducted, for example by a positioning node such as the E-SMLCor the SLP in LTE, or by the UE. The former approach corresponds to theUE-assisted positioning mode, and the latter corresponds to the UE-basedpositioning mode.

In UTRAN Frequency Division Duplex (FDD), an SFN-SFN type 2 measurement(SFN stands for System Frame Number) performed by the UE is used for theOTDOA positioning method. This measurement is the relative timingdifference between cell j and cell i based on the primary Common PilotChannel (CPICH) from cell j and cell i. The UE reported SFN-SFN type 2is used by the network to estimate the UE position.

Positioning Reference Signals

To enable positioning in LTE and facilitate positioning measurements ofa proper quality and for a sufficient number of distinct locations,physical signals dedicated for positioning, such as positioningreference signals (PRS), have been introduced, and low-interferencepositioning subframes have been specified in 3GPP. PRS are transmittedfrom one antenna port R6 according to a pre-defined pattern, asdescribed in more detail below.

A frequency shift, which is a function of a Physical Cell Identity(PCI), can be applied to the specified PRS patterns to generateorthogonal patterns and model an effective frequency reuse of six, whichmakes it possible to significantly reduce neighbor cell interference onthe measured PRS and thus improve positioning measurements. Even thoughPRS have been specifically designed for positioning measurements and ingeneral are characterized by better signal quality than other referencesignals, the standard does not mandate using PRS. Other referencesignals, e.g., cell-specific reference signals (CRS) may also be usedfor positioning measurements.

PRS are transmitted according to a pre-defined pattern and following oneof the pre-defined PRS configurations. PRS are transmitted inpre-defined positioning subframes grouped by a number N_prs ofconsecutive subframes, i.e. one positioning occasion, as illustrated inFIG. 4. Positioning occasions occur periodically with a certainperiodicity of N subframes, corresponding to a time interval T_prsbetween two positioning occasions. The standardized time intervals T_prsare 160, 320, 640, and 1280 ms, and the number of consecutive subframesN_prs are 1, 2, 4, and 6. Each pre-defined PRS configuration comprisesPRS transmission bandwidth, N_prs and T_prs.

OTDOA Assistance Information

Since for OTDOA positioning PRS signals from multiple distinct locationsneed to be measured, the UE receiver often will have to deal with PRSthat are much weaker than those received from the UE's serving cell.Furthermore, without approximate knowledge of when the measured signalsare expected to arrive in time and what is the exact PRS pattern used,the UE would need to do signal search within a large window, which wouldimpact the time and accuracy of the measurements as well as the UEcomplexity. To facilitate UE measurements, assistance information, alsoreferred to as assistance data, is transmitted to the UE, which includese.g. reference cell information, a neighbor cell list containing PCIs ofneighbor cells, the number of consecutive downlink subframes N-prs, PRStransmission bandwidth, and frequency.

The assistance information is signaled over LPP from the positioningserver, e.g., an E-SMLC in the control plane for an LTE system, to theUE.

OTDOA Inter-Frequency Measurements and Measurement Gaps

In LTE OTDOA, the UE measures Reference Signal Time Difference (RSTD)which has been defined in the standard as the relative timing differencebetween cell j and cell i, defined as T_(SubframeRxj)−T_(SubframeRxi),where: T_(SubframeRxj) is the time when the UE receives the start of onesubframe from cell j, T_(SubframeRxi) is the time when the UE receivesthe corresponding start of one subframe from cell i that is closest intime to the subframe received from cell j. The reference point for theobserved subframe time difference shall be the antenna connector of theUE. The measurements are specified for both intra-frequency andinter-frequency and conducted in the RRC_CONNECTED state.

The inter-frequency measurements, including RSTD, are conducted duringperiodic inter-frequency measurement gaps which are configured in such away that each gap starts at an SFN and subframe meeting the followingcondition:

SFN mod T=FLOOR(gapOffset/10);

subframe=gapOffset mod 10;

with T=MGRP/10, where MGRP stands for “measurement gap repetitionperiod” and mod is the modulo function. The E-UTRAN is requiredaccording to the standard to provide a single measurement gap patternwith constant gap duration for concurrent monitoring of all frequencylayers and Radio Access Technologies (RATs). Two configurations areaccording to the standard required to be supported by the UE, with MGRPof 40 and 80 milliseconds (ms), both with a measurement gap length of 6ms. In practice, due to switching time, this leaves less than 6 but atleast 5 full subframes for measurements within each such measurementgap.

In LTE, measurement gaps are configured by the network, i.e. the eNodeB,to enable measurements on different LTE frequencies and/or differentRATs such as e.g., UTRA, GSM and CDMA2000. A measurement is configuredusing the Radio Resource Control (RRC) protocol to signal a measurementconfiguration to the UE. The gap configuration is signaled to the UE aspart of the measurement configuration. Only one gap pattern can beconfigured at a time. The same pattern is used for all types ofconfigured measurements, e.g. inter-frequency neighbor cellmeasurements, inter-frequency positioning measurements, inter-RATneighbor cell measurements, inter-RAT positioning measurements, etc.

In multi-carrier LTE, the inter-frequency measurement gaps are so farintended mainly for performing cell identification and mobilitymeasurements, such as Reference Signal Receiver Power (RSRP) andReference Signal Received Quality (RSRQ). These measurements require aUE to perform measurements over the synchronization signals, i.e., theprimary synchronization signals (PSS) and secondary synchronizationsignals (SSS), and cell-specific reference signals (CRS) to enableinter-frequency handover and enhance system performance. Synchronizationsignals are transmitted over 62 resource elements in the center of theallocated bandwidth in subframes 0 and 5. The PSS is transmitted in thelast OFDM symbol and the SSS is transmitted in the second to last OFDMsymbol of the first slot of a subframe. CRS symbols are transmittedevery subframe and over the entire bandwidth according to one of thestandardized time-frequency patterns. Different cells can use 6different shifts in frequency, and 504 different signals exist. With twotransmit (TX) antennas, the effective reuse for CRS is three.

As can be seen from the above, both synchronization signals and CRS aretransmitted relatively often, although PSS and SSS are transmitted lessfrequently than CRS. This leaves enough freedom when deciding the exacttiming of measurement gaps so that a gap can cover enough symbols withthe signals of interest, i.e., PSS/SSS and/or CRS. With a 6 msmeasurement gap, at most two SSS and two PSS symbols are possible withvery precise timing, while capturing one SSS symbol and one PSS symbolis possible almost without any timing restriction on the measurementgaps since the minimum required effective measurement time is 5 ms onaverage.

In LTE OTDOA, the network, i.e. the eNodeB, can signal a list of cellsoperating on up to three frequency layers, including the serving cellfrequency. The 3GPP RAN4 requirements for RSTD inter-frequencymeasurements are defined for two frequency layers, including the servingcell frequency. Furthermore, the measurement gaps are to be defined suchthat they do not overlap with PRS occasions of the serving cell layer,which would otherwise increase the effective measurement time for boththe serving and the inter-frequency cell. Since the measurement gapsconfigured for the UE are used for RSTD measurements and also formobility measurements, it has been agreed that the pre-defined “GapPattern #0”, which specifies relatively dense and frequent measurementgaps, can be used only when inter-frequency RSTD measurements areconfigured. According to the pre-defined Gap Pattern #0 a measurementgap of 6 ms occurs every 40 ms.

As mentioned above, the measurement gaps to be applied by the UE areconfigured by the eNodeB over RRC. However it is the positioning server,e.g. E-SMLC, which is aware of whether and when the UE will conductpositioning inter-frequency measurements such as e.g., inter-frequencyRSTD or inter-frequency E-CID and this information is transmitted to theUE transparently via the eNodeB. Thus, to be on the safe side the eNodeBmay always configure UEs for the worst case, i.e. for the 40 msmeasurement gap according to the Gap Pattern #0, even when the UEsmeasure only on intra-frequency cells. This is a severe restriction onthe network in that it reduces the amount of radio resources availablefor intra-frequency measurements and it leads to an inefficientmeasurement procedure.

SUMMARY

An object of the present invention is to provide improved methods anddevices for supporting configuration of a measurement gap pattern for auser equipment requiring measurement gaps for performing aninter-frequency measurement for positioning.

The above stated object is achieved by means of methods and devicesaccording to the independent claims.

A first embodiment provides a method in a radio network node of awireless communication system of supporting configuration of ameasurement gap pattern for a user equipment requiring measurement gapsfor performing an inter-frequency measurement for positioning. Themethod comprises receiving, from the user equipment, an indication thatthe user equipment is going to perform an inter-frequency measurementfor positioning and that the inter-frequency measurement requiresmeasurement gaps.

A second embodiment provides a radio network node of a wirelesscommunication system. The radio network node is configured for signalinteraction with a user equipment requiring configuration of ameasurement gap pattern for performing an inter-frequency measurementfor positioning. The radio network node comprises a receiver configuredto receive, from the user equipment, an indication that the userequipment is going to perform an inter-frequency measurement forpositioning and that the inter-frequency measurement requiresmeasurement gaps.

A third embodiment provides a method in a user equipment of a wirelesscommunication system of supporting configuration of a measurement gappattern for an inter-frequency measurement for positioning performed bythe user equipment. The method comprises receiving an indication thatthe user equipment is requested to start an inter-frequency measurementfor positioning for which the user equipment requires measurement gaps.The method also comprises transmitting, to a radio network node, anindication that the user equipment is going to perform aninter-frequency measurement for positioning and that the inter-frequencymeasurement requires measurement gaps.

A fourth embodiment provides a user equipment for use in a wirelesscommunication system. The user equipment is configured for signalinteraction with a radio network node. The user equipment comprises areceiver configured to receive an indication that the user equipment isrequested to start an inter-frequency measurement for positioning forwhich the user equipment requires measurement gaps. The user equipmentalso comprises a transmitter configured to transmit, to a radio networknode, an indication that the user equipment is going to perform aninter-frequency measurement for positioning and that the UE requiresmeasurement gaps for the inter-frequency measurement.

An advantage of some of the embodiments described herein is that byinforming a radio network node that a UE is going to perform aninter-frequency measurement for positioning for which the UE requiresmeasurement gaps, the radio network node is able to configure anappropriate measurement gap pattern for the UE. If the radio networknode is not aware of when the UE is going to perform an inter-frequencymeasurement for positioning for which the UE requires measurement gaps,the radio network node may be required to always configure UEs for ameasurement gap pattern to accommodate inter-frequency measurements forpositioning, even when the UEs measure only on intra-frequency cells.This is a severe restriction on the network in that it reduces theamount of radio resources available for intra-frequency measurements andit leads to inefficient measurement procedures.

Further advantages and features of embodiments of the present inventionwill become apparent when reading the following detailed description inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a cellular communication systemin which embodiments described herein may be implemented.

FIG. 1a is a schematic block diagram of wireless communication system,including a positioning server, in which embodiments described hereinmay be implemented.

FIG. 2 is a schematic block diagram illustrating an LTE system withpositioning functionality.

FIG. 3 is a schematic block diagram illustrating positioning of a userequipment (UE) by determining an intersection of hyperbolascorresponding to measured Reference Signal Time Differences (RSTDs).

FIG. 4 is a schematic block diagram illustrating a measurement gappattern.

FIG. 5 is a schematic block diagram illustrating a Positioning ReferenceSignal pattern when one or two antennas are used for a PhysicalBroadcast Channel (PBCH).

FIG. 6 is a flow diagram illustrating an exemplary embodiment of amethod in a radio network node for supporting configuration of ameasurement gap pattern for a UE requiring measurement gaps forperforming an inter-frequency measurement.

FIG. 7 is a flow diagram illustrating an alternative exemplaryembodiment of a method in a radio network node for supportingconfiguration of a measurement gap pattern for a UE requiringmeasurement gaps for performing an inter-frequency measurement.

FIG. 8 is a flow diagram illustrating an exemplary embodiment of amethod in a UE for supporting configuration of a measurement gap patternfor the UE for performing an inter-frequency measurement.

FIG. 9 is a flow diagram illustrating an alternative exemplaryembodiment of a method in a UE for supporting configuration of ameasurement gap pattern for the UE for performing an inter-frequencymeasurement.

FIG. 10 is a flow diagram illustrating another alternative exemplaryembodiment of a method in a UE for supporting configuration of ameasurement gap pattern for the UE for performing an inter-frequencymeasurement.

FIG. 11 is a schematic block diagram illustrating exemplary embodimentsof a UE and a radio network node.

DETAILED DESCRIPTION

The term “UE” is used throughout this description as a non-limiting termwhich means any wireless device or node, e.g. PDA, laptop, mobile,sensor, fixed relay, mobile relay or even a small base station that isbeing positioned when timing measurements for positioning areconsidered, i.e. a LCS target in general. The UE may also be an advancedUE capable of such advanced features as carrier aggregation, but whichmay still require measurement gaps for performing measurements on atleast some cells and at least some carrier frequency.

A cell is associated with a radio network node, where a radio networknode comprise in a general sense any node capable of transmitting and/orreceiving radio signals that may be used for positioning and/ormeasurements, such as e.g., an eNodeB, macro/micro/pico base station,home eNodeB, relay, beacon device, or repeater. The radio network nodemay be a single-RAT or multi-RAT or multi-standard radio base station.Note that downlink and uplink transmissions do not need to be betweenthe UE and the same radio network node.

A positioning server described in different embodiments is a node withpositioning functionality. For example, for LTE it may be understood asa positioning platform in the user plane, e.g., SLP in LTE, or apositioning server in the control plane, e.g., E-SMLC in LTE. SLP mayalso consist of SLC and SPC, as explained above, where SPC may also havea proprietary interface with E-SMLC. In a testing environment, at leastthe positioning server may be simulated or emulated by test equipment.

The signalling described in the different embodiments is either viadirect links or logical links, e.g. via higher layer protocols such asRRC and/or via one or more network nodes. For example, in LTE in thecase of signalling between E-SM LC and the LCS Client the positioningresult may be transferred via multiple nodes, at least via MME andGateway Mobile Location Centre GMLC.

Herein the term “measurement gap indication” will be used to refer to amessage which indicates a need for measurement gaps for a UE. Themeasurement gap indication may also contain additional information suchas information specifying a frequency to which the measurement relates.There may be a specific measurement gap indications used for a specificpositioning method, e.g. OTDOA.

At least in some embodiments, inter-frequency measurements in thecurrent invention shall be understood in a general sense comprising,e.g., inter-frequency, inter-band, or inter-RAT measurements. Somenon-limiting examples of inter-frequency positioning measurements areinter-frequency E-CID measurements such as UE Rx-Tx time difference,RSRP and RSRQ, and inter-frequency RSTD measurements for OTDOApositioning.

At least some embodiments described herein are not limited to LTE, butmay apply with any RAN, single- or multi-RAT. Some other RAT examplesare LTE-Advanced, UMTS, GSM, cdma2000, WiMAX, and WiFi.

According to current 3GPP standards an eNodeB can use the followingthree different pre-defined measurement gap configurations for a UE toperform inter-frequency and inter-RAT measurements. The inter-frequencymeasurement implies measuring a carrier frequency which is differentfrom that of the serving carrier frequency. The serving carrierfrequency and inter-frequency carrier can both belong to FrequencyDivision Duplex (FDD) mode or Time Division Duplex (TDD) mode or anycombination thereof.

According to a first pre-defined measurement gap configuration, nomeasurement gaps are configured. In this case, the UE is capable ofperforming inter-frequency and/or inter-RAT measurements withoutmeasurement gaps. This may be the case for example, if the UE hasmultiple receivers, which can be activated in parallel. An example isthat of a multi-carrier capable UE, i.e. a UE which is capable ofreceiving data over more than one carrier.

According to a second pre-defined measurement configuration, measurementGap Pattern #0 (also referred to as Gap Pattern 0) is configured. Whenthe UE is configured with the Gap Pattern #0 for performing positioningmeasurements, there is no degradation of the UEinter-frequency/inter-RAT neighbor cell and positioning measurementperformance. This is because according to this pattern the gaps aresignificantly dense and frequent i.e. a gap of 6 ms occurs every 40 ms.This means that the mobility and the positioning, e.g., OTDOA or E-CID,measurement requirements as specified in the standard shall be met.

According to a third pre-defined measurement configuration, measurementGap Pattern #1 (also referred to as Gap Pattern 1) is configured.According to Gap Pattern #1 a gap of 6 ms occurs every 80 ms. There is arisk that UE inter-frequency/inter-RAT neighbor cell and positioningmeasurement performance are degraded if this pattern is used. This isdue to longer periodicity of the occurrence of the measurement gapscompared to the Gap Pattern #0. A consequence could for example besignificantly longer measurement period of one or more of the abovemeasurements in order to meet the corresponding target accuracyrequirements.

It should also be noted that an inter-frequency measurementconfiguration does not include only gap pattern, but also, for example,subframe gap offset and may include other parameters such as the SFNoffset, frame offset etc.

To ensure a desired performance it is desirable that an appropriatemeasurement gap configuration is configured at the UE when positioningmeasurements, e.g., OTDOA measurement such as RSTD, are to be performedby the UE during measurement gaps. In the above E-UTRA example, themeasurement Gap Pattern #0 should be configured when the UE is requestedto measure the inter-frequency RSTD measurement for positioning.Furthermore, to ensure the desired performance it is also desirable thatthe measurement gap configuration is decided such that a sufficientamount of the reference signals, which are used for the positioningmeasurements in measurement gaps, fall in the measurement gaps. InE-UTRAN, the positioning reference signals (PRS) are examples of areference signal.

The objective of configuring an appropriate measurement gap pattern canbe achieved by ensuring that the radio network node, which configuresthe measurement gaps, is aware of that the UE has been requested toperform one or more positioning related measurements, which requiresmeasurement gaps, and of the timing of the occurrence of the referencesignals used for the positioning measurements in gaps.

Examples of information that may be used to indicate timing of theoccurrence of the reference signals are timing offset such as SFNoffset, frame offset, subframe offset or more specifically subframe gapoffset described earlier.

Hence, embodiments described in further detail below provide the radionetwork node with the necessary information pertaining to thepositioning measurements to be done during the measurement gaps in orderto enable the radio network node to configure the appropriatemeasurement gap pattern for performing the positioning measurements.

In case the gaps for the positioning measurements are configured by theeNodeB, in order for the eNodeB to configure appropriate measurementgaps, information related to the measurements for the UE needs to beprovided to or made available at the eNodeB.

As mentioned above FIG. 1a shows a positioning architecture. Asillustrated in FIG. 1a there is an interface 163, e.g. X2, between thetwo eNodeBs 110 a and 110 b and an interface 164 between an eNodeB and anetwork management and/or operation and maintenance (O&M) block 141. Thepositioning node or positioning server 140 is here assumed to be an E-SMLC server in E-UTRAN. The protocol for messaging between the E-SM LC 140and the eNodeBs 110 a is called LPPa. The radio interface protocolbetween the E-SM LC 140 and the UE 150 a, 150 b is called LPP. Note thata link between different network entities may be a physical or a logicallink. A path for higher layer protocols is a logical link which maycomprise one or several physical links.

Assuming an architecture such as shown in FIG. 1 a, exemplaryembodiments will be described. These exemplary embodiments involve gapconfiguration based on explicit indication by the positioning server orUE, implicit indication by assistance data according to which thepositioning server or UE forwards assistance data to the eNodeB, packetsniffing, pre-defined rules and autonomous detection. The solutionsaccording to all embodiments described herein are applicable when the UEis in a non-Discontinuous Receive (DRX) state or in a DRX state. Theembodiments are described in more detail below.

According to an embodiment which involves an explicit indication by thepositioning server, the radio network node, e.g., eNodeB in E-UTRAN,changes or configures the gap configuration(s) for a particular UE,where the configuration is based on the available information regardingthe positioning measurements, e.g., OTDOA RSTD inter-frequencymeasurements or E-CID inter-frequency measurements in E-UTRAN. Theinformation can be cell-specific or specific for a group of UEs or for aparticular UE, and it is provided to the eNodeB by the positioningserver, either on request or without it e.g., by periodic orevent-triggered update. Reception of such information may also be usedto trigger a change of an existing gap configuration in case theexisting configured gap pattern is not appropriate for the positioningmeasurements to be performed.

According to an exemplary embodiment, the positioning server, e.g.E-SMLC, sends a gap configuration switching indicator, cell-specific orUE-specific, to the eNodeB. The gap configuration switching indicatorinstructs the eNodeB to use the appropriate gap configuration for thespecified UEs, a group of UEs or all UEs conducting inter-frequencymeasurements in the cell. The gap configuration switching indicator maye.g. be ‘1’ when inter-frequency measurements are to be used by thespecified UEs, a group of UEs or all UEs conducting inter-frequencymeasurements in the cell. In case the eNodeB is already using a gappattern for a particular UE, which is not appropriate for thepositioning measurement to be performed (e.g., if the pattern isexpected to degrade the performance), then the eNodeB switches theexisting gap pattern for that UE to the appropriate one. The appropriategap pattern is either pre-defined or explicitly indicated by thepositioning server. The positioning server also provides the informationrelated to the carrier frequency over which the positioningmeasurements, e.g., RSTD, are to be performed by the UE(s) inmeasurement gaps. Other information, such as whether the cells on thecarrier frequency are asynchronous or synchronous or timing informationof the reference signals, etc., can also be provided by the positioningserver to the eNodeB, which can use this to determine the mostappropriate gap pattern for the measurements.

The eNodeB may optionally send an acknowledgement (ACK) to the E-SMCL toacknowledge reception of the indicator which is sent by the E-SMLC tothe eNodeB. Thus the E-SMLC receives the ACK if it is used.

Further, according to an exemplary embodiment, the eNodeB sends gapreconfiguration information, e.g., details of gap pattern, subframe gapoffset, frame offset, SFN offset, etc., to the UE by broadcast/multicastor unicast or a UE-specific message, e.g., via RRC signalling, where thegap configuration contains all the necessary and standardizedinformation necessary for the UE to configure measurement gaps. TheeNodeB may also store the gap configuration for each UE. The informationsignalled to the UE can comprise at least a time or a reference pointfrom when the gap configuration shall apply, and/or a measurement gapconfiguration as such.

In a variation of the embodiment of explicit indication to the eNodeB,the eNodeB receives the information necessary for gap reconfigurationfrom a Network Management (NM) and O&M node 141 instead of from thepositioning server 140. In this case, information originating from thepositioning node 140 is also communicated to the NM and O&M node 141.

In a further variation of the embodiment of explicit indication to theeNodeB, the eNodeB receives the information necessary for appropriatemeasurement gap configuration or reconfiguration from the UE. The UE ismade aware of that it is going to perform an inter-frequency measurementfor positioning when the positioning server requests such measurementsfrom the UE. Accordingly the UE may signal an explicit indication toindicate to the radio network node that it requires measurement gaps.

According to an embodiment which involves implicit indication,assistance data is forwarded to the eNodeB to inform the eNodeB that theUE will be performing a measurement for which measurement gaps need tobe configured. According to one alternative, the positioning server 140signals the assistance data or certain elements of the assistance datafor each UE or group of UEs to the radio network node. In the E-UTRANexample illustrated in FIG. 1a this means that the E-SMLC 140 signalsthe assistance data or part of it to the eNodeB 110 a or 110 b over theLPPa protocol. The eNodeB 110 a/b may also send an acknowledgementmessage to the E-SM LC in the same way as explained above for theexemplary embodiment with an explicit indication. The elements of theassistance data that is signalled to the eNodeB will according to anexemplary embodiment contain at least information related to the carrierfrequencies of the cells which are to be used for the positioningmeasurements. The radio network node (i.e. the eNodeB in this example)is aware of the serving carrier frequency f1 of the UE. In case theassistance data received by the radio network node contains more thanone carrier frequency, e.g., f1 and f2, or if it contains one or morecarrier frequencies f2 which are different than that of the servingcarrier frequency, then the radio network node can use this informationto deduce that the UE is requested to do inter-frequency measurementsfor positioning, e.g. inter-frequency RSTD measurements. Thesemeasurements are carried out by the UE in measurement gaps. Hence theeNodeB may use this information to configure the measurement gaps, whichare relevant for the positioning measurements to be performed in themeasurement gaps. In E-UTRAN, this means that the eNodeB can use thereceived assistance data or part of it and e.g. configure Gap Pattern 0or modify an existing Gap Pattern 1 to the Gap Pattern 0 for allmeasurements to be performed in measurement gaps. The configuration ormodification of the measurement gaps can be done in the same manner asexplained above. Accordingly the radio network node may signalinformation to the UE to initiate use of an appropriate gap pattern inthe UE. The information signalled to the UE may e.g. comprise adetermined measurement gap pattern, an indication of or reference to apre-defined measurement gap pattern, and/or a time or reference pointfrom when the measurement pattern to be configured is to apply.

The assistance data is sent from the positioning server 140 to the UE150 a or 150 b in order to facilitate the UE to perform the positioningmeasurements, e.g., RSTD in case of OTDOA or signal strength/qualitymeasurements for enhanced cell ID, etc. For example in E-UTRAN, theassistance data is sent to the UE over the LPP protocol and is specifiedin section 6.5.1.2 in 3GPP TS 36.355 V 9.1.0 (2010 March), EvolvedUniversal Terrestrial Radio Access (E-UTRA); LTE Positioning Protocol(LPP) (Release 9). Since the LPP protocol is between the UE and theE-SMLC the eNodeB does not receive the assistance data when it istransmitted from the E-SMLC to the UE. As explained above, the idea ofthe above described embodiment is that the assistance data or a part ofthe assistance data, which is sent to the UE, is also forwarded by thepositioning node to the radio network node, e.g., eNodeB. In a variationof this embodiment the assistance data or part of the assistance data isforwarded to the radio network node by the UE. According to an examplethe data elements that are sent to the eNodeB are UE specific, sent overLPPa and are the data elements of the information elementOTDOA-NeighbourCelllnfoList specified in section 6.5.1.2 in 3GPP TS36.355 cited above as follows:

-   -   “OTDOA-NeighbourCellInfoList

The IE OTDOA-NeighbourCellInfoList is used by the location server toprovide neighbour cell information for OTDOA assistance data. TheOTDOA-NeighbourCellInfoList is sorted according to best measurementgeometry at the a priori location estimate of the target device. I.e.,the target device is expected to provide measurements in increasingneighbor cell list order (to the extent that this information isavailable to the target device).

-- ASN1START OTDOA-NeighbourCellInfoList ::= SEQUENCE (SIZE(1..maxFreqLayers) ) OF OTDOA-NeighbourFreqInfo OTDOA-NeighbourFreqInfo::= SEQUENCE (SIZE (1..24) ) OF OTDOA- NeighbourCellInfoElementOTDOA-NeighbourCellInfoElement ::= SEQUENCE {  physCellId  INTEGER(0..503),  cellGlobalId  ECGI    OPTIONAL,  earfcn  ARFCN-ValueEUTRAOPTIONAL,    -- Cond NotSameAsRef0  cpLength  ENUMERATED {normal,extended, . . . }   OPTIONAL,                  -- Cond NotSameAsRef1 prsInfo  PRS-Info    OPTIONAL,        -- Cond NotSameAsRef2antennaPortConfig ENUMERATED {ports-1-or-2, ports-4, . . . }           OPTIONAL,         -- Cond NotsameAsRef3  slotNumberOffsetINTEGER(0..31)   OPTIONAL,    -- Cond NotSameAsRef4  prs-SubframeOffset INTEGER (0..1279) OPTIONAL,      -- Cond InterFreq  expectedRSTD INTEGER (0..16383),  expectedRSTD-Uncertainty  INTEGER (0..1023),  . .. } maxFreqLayers INTEGER ::= 3 --ASN1STOP”

It can be seen above that the information element contains carrierfrequency information since “earfcn” is the frequency channel of theconcerned cell. The eNodeB can use this information, e.g. if there is atleast a carrier which is different than that of the serving carrier, todeduce whether the UE is required to perform positioning measurements,e.g., RSTD measurements, in measurement gaps or not. Accordingly theeNodeB can ensure that relevant measurement gaps are configured tofacilitate measurements in gaps, such as inter-frequency RSTDmeasurements etc. Similarly the assistance data or part of it, such ascarrier frequency information, related to other positioning methods thanOTDOA, like e.g. enhanced cell ID can also be signalled to the eNodeB bythe positioning sever or by the UE.

An alternative exemplary embodiment, which now will be explained,involves packet sniffing. This embodiment is useful in case the eNodeBdoes not have explicit or implicit information about the positioningmeasurements to be carried out by the UE during measurement gaps. Henceall actions including the determination whether a particular UE performsthe inter-frequency measurements are performed by the eNodeB or theradio network node which configures the measurement gaps. If the radionetwork node which configures the measurement gaps is an eNodeB, theeNodeB can sniff packets with LPP or similar messages which are sent tothe UE by the positioning sever. The sniffed messages may contain theassistance information to be used by the UE for performing thepositioning measurements, e.g., inter-frequency carrier etc. Themessages which contain the assistance information pass over the eNodeBtransparently. Hence the eNodeB can sniff these messages. The assistanceinformation which is acquired by sniffing enables the eNodeB to decidewhether to configure a measurement gap pattern for performinginter-frequency positioning measurements or not. The measurement gappattern may e.g. be a gap pattern which is pre-defined for positioningmeasurements such as Gap Pattern #0. For example, if the eNodeB detectsby sniffing the assistance information that there are at least two cellsin the assistance data operating on different frequencies, e.g., cell 1and cell 2 operating on frequencies f1 and f2 respectively, then theeNodeB can assume that measurement gaps are needed for the positioningmeasurements. In addition the eNodeB knows the serving carrier frequencyf1, which means that the eNodeB can assume that f2 is theinter-frequency. Hence the eNodeB will configure a measurement gappattern, or adjust an existing measurement gap pattern in case ameasurement gap pattern is already in operation, to ensure thatsufficient amount of the reference signals on carrier f2 fall within themeasurements gaps of the configured or adjusted measurement gap pattern.The reference signal may e.g. be PRS on f2 and the measurement gappattern may e.g. be configured or adjusted such that at least onesub-frame containing the reference signal falls within the measurementgaps. The configuration of the measurement gap patterns in the UE can becarried out in the same way as described above irrespective of whetherthe radio network node is made aware of the UE's need for measurementgaps for performing an inter-frequency measurement for positioning bymeans of sniffing or by means of another method such as explicit orimplicit indication from the positioning server or the UE.

Another alternative embodiment involves a pre-defined rule in the UE.When assistance data is received by the UE, e.g., via LPP, and the UEwill conduct inter-frequency measurements or another type ofmeasurements in measurement gaps for carrier f1 and carrier f2 then theUE itself reconfigures the measurement gaps which are most relevant forthe measurements to be performed. The carriers f1 and f2 can be given inthe field ‘earfcn’ of the assistance data as mentioned above. Themeasurement gap to be configured or re-configured can be pre-defined ina standard. Accordingly the UE can configure the measurement gaps byitself following one or several pre-defined rules. The followingpre-defined set of rules can for example be used:

If exist f2≠f1  If (current_status==no_gaps)   change to: gapconfiguration #0,  if (current_status==gap_configuration #1)   −> changeto: gap configuration #0,  Otherwise, no change.

The above exemplary pre-defined set of rules means that the UE changes acurrent gap configuration to the pre-defined gap pattern configuration,which is appropriate for the positioning measurements to be done in themeasurement gaps, e.g., inter-frequency measurements.

In a variation of this embodiment, if the solution of pre-defined rulesfor the UE is used, the UE can indicate to the eNodeB that “positioningongoing” and that it needs the Gap Pattern 0. When positioning is nolonger wanted the UE can update the eNodeB again. This information“positioning ongoing” can be transferred over an X2 interface as well,e.g., to a node associated with the new serving cell of the UE when theUE performs handover, or to a neighbour node to indicate a measurementgap pattern for positioning measurements used in this cell.

Yet another exemplary embodiment involves autonomous detection in anetwork node. In case RS or PRS used by the UE for performingpositioning measurements are configured on more than one carrierfrequency in the eNodeB, then the eNodeB may be configured to always usethe most appropriate gap pattern required for performing positioningmeasurements, e.g., the eNodeB configures only Gap Pattern 0 for allmeasurements in E-UTRAN. The eNodeB assumes that measurements on atleast one of the carrier frequencies are done in gaps. Secondly themeasurement gaps are configured to ensure that as many PRS sub-frames aspossible on different carriers lie in the measurement gaps. Thisembodiment is useful in case the eNodeB does not have any other means todetermine whether positioning measurements are done in measurement gapsor not for a particular UE.

A further exemplary embodiment involves using an X2 interface forspecifically exchanging the information about cells on frequencies usedfor positioning. It is possible in LTE for eNodeBs to exchangeinformation over the X2 interface. The information can be, for example,a list of all bandwidths over all carriers in the associated cells.According to this embodiment the eNodeBs, in addition to the carrierinformation also include information on whether the carrier is used forpositioning measurements e.g., whether frequency f1 is used for PRStransmissions and/or configuring positioning subframes or the UEsconduct positioning measurements on CRS. In another embodiment, PRStransmission bandwidth is also exchanged via X2.

Yet a further exemplary embodiment involves applying a defaultmeasurement gap configuration. Examples of default configurations whichmay be applied are:

-   -   In a multi-RAT and/or multi-frequency system, when sites are        co-located, the eNodeB can decide to use Gap Pattern 0 when        different cells of the site are operating on different        frequencies/RATs.    -   Gap Pattern 0 is always used as a default gap configuration in        an eNodeB when the network provides positioning services.    -   Gap Pattern 0 is used as a default configuration in an eNodeB        when PRS is transmitted.    -   Configuration of Gap pattern 0 is triggered by a positioning        request.    -   The Gap configuration, e.g., gap pattern, of an eNodeB can be        decided and configured by another node, e.g., the NM and/ O&M        node 141, a Self Organizing Network (SON) node, a macro eNodeB,        etc.

The default gap configuration is used by the eNodeB when configuring theUE for inter-frequency measurements. In one embodiment, the eNodeBreconfigures the UEs to the new default gap configuration in one of theevents listed above and the default configuration changes.

The embodiments described above enjoy a number of advantages overprevious methods and apparatus, including, for example, solving theproblem of incomplete support for inter-frequency measurements.

Some of the embodiments described above involves that the UE indicates aneed for measurement gaps to the radio network node. Such an indicationmay be signaled to the radio network node by means of RRC signaling. Anadvantage of the UE sending the indication, rather than the positioningserver, is that this embodiment is applicable for user plane positioningas well as for control plane positioning. It is not certain that thepositioning server knows if the UE actually requires measurement gaps,since the positioning server might not have full knowledge of the UEscapabilities. Accordingly an advantage of having the UE itself indicateits need for measurement gaps is that it reduces the risk of configuringmeasurement gaps in cases where the UE does not require measurementgaps.

FIG. 6 is a flow diagram of a method in a radio network node forsupporting configuration of a measurement gap pattern for a UE requiringmeasurement gaps for performing an inter-frequency measurement. Themethod comprises receiving, in a step 71, from the UE an indication thatthe UE is going to perform an inter-frequency measurement forpositioning and that the inter-frequency measurement requiresmeasurement gaps. The inter-frequency measurement may e.g. be aReference Signal Time Difference, RSTD, measurement. The receivedindication may include an indication of a measurement gap pattern thatthe UE needs for performing the inter-frequency measurement. Such anindication may be an indication of a need for configuring a pre-definedmeasurement gap pattern, such as Gap Pattern #0 which specifies a gap of6 ms that occurs every 40 ms.

FIG. 7 is a flow diagram illustrating an alternative embodiment in aradio network node for supporting configuration of a measurement gappattern for a UE requiring measurement gaps for performing aninter-frequency measurement. The step 71 in which the radio network nodereceives, from the user equipment, an indication that the UE is going toperform an inter-frequency measurement for positioning and that theinter-frequency measurement requires measurement gaps, is the same asexplained above in connection with FIG. 6. The method in FIG. 7 alsocomprises a step 73, in which the radio network node determines, basedon the received indication, a measurement gap pattern for performing theinter-frequency measurement. A further step 74 comprises signaling tothe UE information to initiate use of the determined measurement gappattern in the UE. The information that is signaled to the UE may e.g.include a time or reference point from when the determined gap patternis to apply and/or the determined measurement gap pattern. Theinformation signaled to the UE may e.g. specify gap offset and/or apattern activation time to be applied.

According to further variations of the embodiments illustrated in FIG. 6and FIG. 7 the radio network node may store information on thedetermined measurement gap pattern associated with the UE. Thus theradio network node may store information on different measurement gappatterns configured for different UEs. In another variation the radionetwork node receives from the UE an indication that the user equipmentis going to stop the inter-frequency measurement. Thus the radio networknode is informed that the UE no longer needs the measurement gap patternfor performing the inter-frequency measurement.

FIG. 8 is a flow diagram of a method in a UE for supportingconfiguration of a measurement gap pattern for an inter-frequencymeasurement performed by the UE. The method comprises receiving anindication that the user equipment is requested to start aninter-frequency measurement for positioning for which the user equipmentrequires measurement gaps in a step 101. The indication that the UE isrequested to start an inter-frequency measurement may be received from apositioning server such as an E-SMCL or SLP. In a step 102, the UEtransmits, to a radio network node, an indication that the UE is goingto perform an inter-frequency measurement for positioning and that theinter-frequency measurement requires measurement gaps. If the UE hascapabilities for performing the inter-frequency measurement withoutmeasurement gaps it should not indicate to the radio network node thatit requires measurement gaps for performing the inter-frequencymeasurement. The indication transmitted to the radio network node mayinclude an indication of a measurement gap pattern that the userequipment needs for performing the inter-frequency measurement. In avariation of the illustrated embodiment, the UE also transmits to theradio network node an additional indication that indicates that the userequipment is going stop the inter-frequency measurement. The indicationmay apply for one or more pre-defined positioning methods, e.g., OTDOAand/or E-CID.

As described above there are embodiments in which the radio network nodeconfigures the measurement gap pattern to be applied by the UE and otherembodiments in which the UE itself configures the measurement gappattern based on pre-defined rules in the UE. FIGS. 9 and 10 are flowdiagrams illustrating embodiments according to these differentalternatives.

FIG. 9 illustrates a method in which the UE itself configures ameasurement gap pattern to be used for inter-frequency positioningmeasurements. The method comprises the steps 101 and 102 which are thesame as described above in connection with FIG. 8. In addition themethod comprises a step 103 in which the UE determines the measurementgap pattern to be used for performing the inter-frequency measurement.The step 103 is initiated in response to receiving the indication thatthe UE is requested to perform the inter-frequency measurement. The UEdetermines the measurement gap pattern based on a pre-defined set ofrules. In a step 104 the determined measurement gap pattern isconfigured in the UE.

FIG. 10 illustrates a method in which the UE receives information on thedetermined measurement gap configuration from the radio network node.The method comprises the steps 101 and 102 which are the same asdescribed above in connection with FIG. 8. In addition the methodcomprises a step 105 in which the UE receives from the radio networknode information indicating a determined measurement gap pattern to beused for performing the inter-frequency measurement. In a step 106 theUE uses the determined measurement gap pattern.

In a variation the methods illustrated in FIGS. 9 and 10 also includesas step in which the UE determines based on the UE's capabilities thatit requires measurement gaps to perform the inter-frequency measurementfor positioning. If the UE is capable of performing the inter-frequencymeasurement for positioning, the UE should of course not send anyindication to the radio network node that it requires measurement gapsfor performing the inter-frequency measurement for positioning.

FIG. 11 is a schematic block diagram illustrating exemplary embodimentsof a radio network node 81 and a UE 91 respectively, which may beconfigure to perform the methods illustrated in FIGS. 6-10.

The radio network node 81 comprises a receiver 82, a processor 83, atransmitter 84, and at least one antenna 89 and a memory 88. Thereceiver 82 may be configured to receive an indication 85 that indicatesthat UE is to perform an inter-frequency measurement for which the UErequires measurement gaps. The processor 83 may be configured todetermine the measurement gap pattern based on the indication 85 and thetransmitter 84 may be configured to transmit information 86 to the UE toinitiate use of the determined measurement gap pattern. The memory 88may store information on determined measurement gap patterns fordifferent UEs.

The UE 91 comprises a receiver 92, a processor 93, a transmitter 94, andat least one antenna 95. The receiver 92 is configured to receive anindication 87, e.g. from a positioning server, which indicates, that theUE is requested for perform an inter-frequency measurement. Thetransmitter 94 is configured to transmit the indication 85 to the radionetwork node 81. The processor 93 may be configured to determine themeasurement gap pattern to be applied according to a set of pre-definedrules.

The functional blocks depicted in FIG. 11 can be combined andre-arranged in a variety of equivalent ways, and many of the functionscan be performed by one or more suitably programmed digital signalprocessors and other known electronic circuits e.g., discrete logicgates interconnected to perform a specialized function, orapplication-specific integrated circuits. Moreover, connections amongand information provided or exchanged by the functional blocks depictedin FIG. 11 can be altered in various ways to enable a radio network nodeand a UE respectively to implement the methods described above and othermethods involved in the operation of the radio network node or the UE ina wireless communication system.

Many aspects of the embodiments presented herein are described in termsof sequences of actions that can be performed by, for example, elementsof a programmable computer system. Embodiments of UEs include, forexample, mobile telephones, pagers, headsets, laptop computers and othermobile terminals, and the like. Moreover, some embodiments describedherein can additionally be considered to be embodied entirely within anyform of computer-readable storage medium having stored therein anappropriate set of instructions for use by or in connection with aninstruction-execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch instructions from a medium and execute the instructions. Asused here, a “computer-readable medium” can be any means that cancontain, store, or transport the program for use by or in connectionwith the instruction-execution system, apparatus, or device. Thecomputer-readable medium can be, for example but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device. More specific examples (anon-exhaustive list) of the computer-readable medium include anelectrical connection having one or more wires, a portable computerdiskette, a random-access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), and anoptical fiber. Thus, there are numerous different embodiments in manydifferent forms, not all of which are described above, that fall withinthe scope of the appended claims. For each of the various aspects, anysuch form may be referred to as “logic configured to” perform adescribed action, or alternatively as “logic that” performs a describedaction.

Several of the embodiments described above use an LTE scenario as anexemplary application scenario. LTE standard specifications can be seenas an evolution of the current wideband code division multiple access(WCDMA) specifications. An LTE system uses orthogonal frequency divisionmultiplex (OFDM) as a multiple access technique (called OFDMA) in adownlink (DL) from system nodes to user equipments (UEs). An LTE systemhas channel bandwidths ranging from about 1.4 MHz to 20 MHz, andsupports throughputs of more than 100 megabits per second (Mb/s) on thelargest-bandwidth channels. One type of physical channel defined for theLTE downlink is the physical downlink shared channel (PDSCH), whichconveys information from higher layers in the LTE protocol stack and towhich one or more specific transport channels are mapped. Controlinformation is conveyed by a physical uplink control channel (PUCCH) andby a physical downlink control channel (PDCCH). LTE channels aredescribed in 3GPP Technical Specification (TS) 36.211 V9.1.0, PhysicalChannels and Modulation (Release 9) (Dec. 2009), among otherspecifications.

An IMT-Advanced communication system uses an internet protocol (IP)multimedia subsystem (IMS) of an LTE, HSPA, or other communicationsystem for IMS multimedia telephony (IMT). In the IMT advanced system(which may be called a “fourth generation” (4G) mobile communicationsystem), bandwidths of 100 MHz and larger are being considered. The 3GPPpromulgates the LTE, HSPA, WCDMA, and IMT specifications, andspecifications that standardize other kinds of cellular wirelesscommunication systems.

In an OFDMA communication system, the data stream to be transmitted isportioned among a number of narrowband subcarriers that are transmittedin parallel. In general, a resource block devoted to a particular UE isa particular number of particular subcarriers used for a particularperiod of time. Different groups of subcarriers can be used at differenttimes for different users. Because each subcarrier is narrowband, eachcarrier experiences mainly flat fading, which makes it easier for a UEto demodulate each subcarrier. OFDMA communication systems are describedin the literature, for example, U.S. Patent Application Publication No.US 2008/0031368 A1 by B. Lindoff et al.

FIG. 1 depicts a typical cellular communication system 10. Radio networkcontrollers (RNCs) 12, 14 control various radio network functions,including for example radio access bearer setup, diversity handover,etc. In general, each RNC directs calls to and from a UE, such as amobile station (MS), mobile phone, or other remote terminal, viaappropriate base station(s) (BSs), which communicate with each otherthrough DL (or forward) and uplink (UL, or reverse) channels. In FIG. 1,RNC 12 is shown coupled to BSs 16, 18, 20, and RNC 14 is shown coupledto BSs 22, 24, 26. Each BS, or eNodeB which is a BS in an LTE system,serves a geographical area that is divided into one or more cell(s). InFIG. 1, BS 26 is shown as having five antenna sectors S1-S5, which canbe said to make up the cell of the BS 26, although a sector or otherarea served by signals from a BS can also be called a cell. In addition,a BS may use more than one antenna to transmit signals to a UE. The BSsare typically coupled to their corresponding RNCs by dedicated telephonelines, optical fiber links, microwave links, etc. The RNCs 12, 14 areconnected with external networks such as the public switched telephonenetwork (PSTN), the internet, etc. through one or more core networknodes, such as a mobile switching center (not shown) and/or a packetradio service node (not shown).

It will be understood that the arrangement of functionalities depictedin FIG. 1 can be modified in LTE and other communication systems. Forexample, the functionality of the RNCs 12, 14 can be moved to theeNodeBs 22, 24, 26, and other functionalities can be moved to othernodes in the network. It will also be understood that a base station canuse multiple transmit antennas to transmit information into acell/sector/area, and those different transmit antennas can sendrespective, different pilot signals.

The use of multiple antennas plays an important role in modern wirelesscommunication systems, such as LTE systems, to achieve improved systemperformance, including capacity and coverage, and service provisioning.Acquisition of channel state information (CSI) at the transmitter or thereceiver is important to proper implementation of multi-antennatechniques. In general, channel characteristics, such as the impulseresponse, are estimated by sending and receiving one or more predefinedtraining sequences, which can also be called reference signals. Toestimate the channel characteristics of a DL for example, a BS transmitsreference signals to UEs, which use the received versions of the knownreference signals to estimate the DL channel. The UEs can then use theestimated channel matrix for coherent demodulation of the received DLsignal, and obtain the potential beam-forming gain, spatial diversitygain, and spatial multiplexing gain available with multiple antennas. Inaddition, the reference signals can be used to do channel qualitymeasurement to support link adaptation.

In the case of OFDM transmission, a straightforward design of areference signal is to transmit known reference symbols in the OFDMfrequency-vs.-time grid. Cell-specific reference signals and symbols aredescribed in Clauses 6.10 and 6.11 of 3GPP TS 36.211 V9.0.0, EvolvedUniversal Terrestrial Radio Access (E-UTRA), Physical Channels andModulation (Release 9) (December 2009). Up to four cell-specificreference signals corresponding to up to four transmit antennas of aneNodeB are specified. Such reference signals are used by the eNodeB forcodebook-based, multiple-stream, spatial multiplex transmission. Acodebook is a predefined finite set of a number of precoding matriceshaving different ranks. In codebook based precoding, the UE estimatesthe channel matrix based on the cell-specific reference signals, carriesout an exhaustive search over all precoding matrices, and reports apreferred precoding matrix indicator (PMI) to the eNodeB according tocertain criteria, thereby maximizing system throughput, etc. The PMIdetermined by a UE can be overridden by the eNodeB.

3GPP TS 36.211 also defines a UE-specific reference signal on an antennaport 5 that is transmitted only on resource blocks upon which acorresponding physical downlink shared channel (PDSCH) is mapped. TheUE-specific reference signal supports non-codebook based, single-streambeamforming transmission. In non-codebook based precoding, the precodingweight matrix applied both on UE-specific reference symbols and the datasymbols is not from the codebook set but is directly calculated by theeNodeB in terms of various criteria, e.g., the weight matrix can becalculated based on eigen decomposition or on direction of arrival. In atime-division duplex (TDD) system, due to channel reciprocity,non-codebook based beamforming/precoding can reduce further uplinkfeedbacks and improve beamforming gain.

The DL of a LTE system can use both codebook-based precoding andnon-codebook based beamforming/precoding for up to four transmitantennas. The transmission mode switch between codebook-based,multiple-stream spatial multiplexing transmission andnon-codebook-based, single-stream beamforming transmission issemi-statically configured via higher layer signaling.

Some communication systems, such as LTE-Advanced that is currently beingspecified by 3GPP, can employ more than four transmit antennas in orderto reach more aggressive performance targets. For example, a systemhaving eNodeBs with eight transmit antennas need extension of currentLTE codebook-based precoding from precoder and reference signalperspectives.

PRS are transmitted from one antenna port (R6) according to apre-defined pattern, as described for example in Clause 6.10.4 of 3GPPTS 36.211 V9.0.0, Evolved Universal Terrestrial Radio Access (E-UTRA),Physical Channels and Modulation (Release 9) (December 2009). One of thecurrently agreed PRS patterns is shown in FIG. 5, which corresponds tothe left-hand side of FIG. 6.10.4.2-1 of 3GPP TS 36.211, where thesquares containing R₆ indicate PRS resource elements within a block oftwelve subcarriers over fourteen OFDM symbols (i.e., a 1-ms subframewith normal cyclic prefix).

A set of frequency shifts can be applied to the pre-defined PRS patternsto obtain a set of orthogonal patterns which can be used in neighborcells to reduce interference on the PRS and thus improve positioningmeasurements. The effective frequency reuse of six can be modelled inthis way. The frequency shift is defined as a function of Physical CellID (PCI) as follows:

v _(shift)=mod(PCI,6)

in which v^(shift) is the frequency shift, mod( ) is the modulofunction, and PCI is the Physical Cell ID. The PRS can also betransmitted with zero power, or muted.

To improve hearability of the PRS, i.e., to enable detecting the PRSfrom multiple sites and with a reasonable quality, positioning subframeshave been designed as low-interference subframes, i.e., it has also beenagreed that no data transmissions are allowed in general in positioningsubframes. As a result, synchronous networks' PRS are ideally interferedwith only by PRS from other cells having the same PRS pattern index,i.e., the same vertical shift (v_shift), and not by data transmissions.

In partially aligned asynchronous networks, PRS can still be interferedwith by transmissions over data channels, control channels, and anyphysical signals when positioning subframes collide with normalsubframes, although the interference is reduced by the partialalignment, i.e., by aligning the beginnings of positioning subframes inmultiple cells within one-half of a subframe with respect to some timebase. PRS are transmitted in pre-defined positioning subframes groupedby several consecutive subframes (N_(PRS)), i.e., one positioningoccasion, which occur periodically with a certain periodicity of Nsubframes, i.e., the time interval between two positioning occasions.The currently agreed periods N are 160, 320, 640, and 1280 ms, and thenumber of consecutive subframes N_(PRS) can be 1, 2, 4, or 6, asdescribed in 3GPP TS 36.211 cited above.

As described above, methods and apparatus according to the embodimentspresented above include, but are not limited to, one or more of thefollowing aspects: signalling to support gap configuration, methods forgap configuration and using an X2 interface for exchanging theinformation on the frequency used for positioning measurements.

In addition, embodiments described above can be incorporated in user-and/or control-plane positioning solutions, although the latter iscurrently believed to be more common, and in other positioning methodsand their hybrids, in addition to OTDOA and E-CID. It will be understoodthat this description is given in terms of an eNodeB as the radionetwork node, but the invention can be embodied in other types of radionetwork nodes, e.g., pico BSs, home NodeBs, etc.

1. A method in a user equipment of a wireless communication system, themethod comprising: transmitting, to a radio access network, anindication that the user equipment is going to start an inter-frequencypositioning measurement which requires measurement gaps; and startingthe inter-frequency positioning measurement according to the indication.2. The method of claim 1, wherein the inter-frequency positioningmeasurement is an observed time difference of arrival (OTDOA)inter-frequency reference signal time difference (RSTD) measurement. 3.The method of claim 1, wherein the indication is included in a radioresource control (RRC) message transmitted from the user equipment tothe radio access network.
 4. The method of claim 1, comprisingtransmitting the indication responsive to receiving signaling from apositioning server indicating that the user equipment is to start theinter-frequency positioning measurement.
 5. The method of claim 1,further comprising transmitting, to the radio access network, a subframegap offset defining a measurement gap within which the user equipment isgoing to perform the inter-frequency positioning measurement whichrequires measurement gaps.
 6. The method of claims 1, furthercomprising, after starting the inter-frequency positioning measurement,transmitting, to the radio access network, an indication that the userequipment is going to stop the inter-frequency positioning measurementwhich requires measurement gaps.
 7. A user equipment configured for usein a wireless communication system, the user equipment comprising: atransmitter; and processing circuitry configured to: transmit, via thetransmitter and to a radio access network, an indication that the userequipment is going to start an inter-frequency positioning measurementwhich requires measurement gaps; and start the inter-frequencypositioning measurement according to the indication.
 8. The userequipment of claim 7, wherein the inter-frequency positioningmeasurement is an observed time difference of arrival (OTDOA)inter-frequency reference signal time difference (RSTD) measurement. 9.The user equipment of claim 7, wherein the indication is included in aradio resource control (RRC) message transmitted from the user equipmentto the radio access network.
 10. The user equipment of claim 7, whereinthe processing circuitry is configured to transmit, via the transmitter,the indication responsive to receiving signaling from a positioningserver indicating that the user equipment is to start theinter-frequency positioning measurement.
 11. The user equipment of claim7, wherein the processing circuitry is further configured to transmit,via the transmitter, a subframe gap offset defining a measurement gapwithin which the user equipment is going to perform the inter-frequencypositioning measurement which requires measurement gaps.
 12. The userequipment of claim 7, wherein the processing circuitry is furtherconfigured to, after starting the inter-frequency positioningmeasurement, transmit, via the transmitter and to the radio accessnetwork, an indication that the user equipment is going to stop theinter-frequency positioning measurement which requires measurement gaps.13. A radio network node configured for use in a wireless communicationsystem, the radio network node comprising: a receiver; a transmitter;and processing circuitry configured to: receive, via the receiver andfrom a user equipment, an indication that the user equipment is going tostart an inter-frequency positioning measurement which requiresmeasurement gaps; and transmit, via the transmitter and to the userequipment, information specifying a configuration of measurement gapsfor the user equipment to perform the inter-frequency positioningmeasurement.
 12. The radio network node of claim 13, wherein theinter-frequency positioning measurement is an observed time differenceof arrival (OTDOA) inter-frequency reference signal time difference(RSTD) measurement.
 13. The radio network node of claim 13, wherein theindication is included in a radio resource control (RRC) messagereceived at the radio access node from the user equipment.
 14. The radionetwork node of claim 13, wherein the processing circuitry is furtherconfigured to receive, via the receiver and from the user equipment, asubframe gap offset defining a measurement gap within which the userequipment is going to perform the inter-frequency positioningmeasurement which requires measurement gaps.
 15. The radio network nodeof claim 14, wherein the processing circuitry is further configured todetermine the configuration of measurement gaps based on the subframegap offset.
 16. The radio network node of claim 13, wherein theprocessing circuitry is further configured to receive, via the receiverand from the user equipment, an indication that the user equipment isgoing to stop the inter-frequency positioning measurement which requiresmeasurement gaps.